In mathematics, the Alperin–Brauer–Gorenstein theorem characterizes the finite simple groups with quasidihedral or wreathed[1] Sylow 2-subgroups.
These are isomorphic either to three-dimensional projective special linear groups or projective special unitary groups over a finite field of odd order, depending on a certain congruence, or to the Mathieu group
Alperin, Brauer & Gorenstein (1970) proved this in the course of 261 pages.
The subdivision by 2-fusion is sketched there, given as an exercise in Gorenstein (1968, Ch.
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